Total Lunar Eclipse: Cloud forecast

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  • Many will be hoping for cloudless skies in the early hours of Monday morning. Photo: David Cheskin/PA Archive/PA Images.

    Surface pressure chart for midnight Sunday showing the influence of high pressure.

    The orange/red hue is characteristic of a total lunar eclipse. Photo: Phil Noble/PA Archive/PA Images.

  • Total Lunar Eclipse: Cloud forecast
    24.09.2015 13:51

     

    It will be an exciting night for astronomers and keen observers alike this Sunday as the last total lunar eclipse for three years occurs, affording a glimpse at one of the more spectacular stellar events. However, the weather can be a frustrating factor in obscuring celestial episodes from the ground, so prior consideration of the forecast can be crucial to ensure a good location is chosen to view the eclipse.

    A total lunar eclipse occurs when there is an almost complete alignment of the sun, earth and moon (with the earth in the middle), so that the moon moves directly across the earth’s umbra (or shadow). The scattering of light through the atmosphere ensures that only long wavelengths in the form of orange and red colours are refracted to the moon, which is why is also termed a ‘blood moon’. In the UK, it will have to be for the more committed folk to view since the moon will start encroaching the earth’s umbra from 02:07 BST on Monday, with the duration of the total eclipse from 03:11 to 04:23 (mid-eclipse being 03:47).

    So how is the weather shaping up for the event? The dominant synoptic set up will be relatively unchanged through the weekend as a large area of high pressure extends across the UK bringing predominantly dry and settled conditions. The problem with high pressure, however, is that weather models tend to be quite poor at resolving the amount of cloud under sinking air. There is reasonable agreement that north-western parts of the UK are likely to see the greatest cloud cover, but it may be rather variable elsewhere. This will be compounded by the likelihood of mist and fog developing in places, a common feature under high pressure in the autumn as the nights draw longer and overnight temperatures fall lower.

    The best estimate for cloud cover will be nearer to the event, as this is the time when weather models typically operate with greatest accuracy. Make sure to use the interactive map at www.meteoearth.com to keep tabs on the latest forecast.

    By: Nick Prebble